I suppose it depends on your passport/nationality. For me (EU) it appears more to be a revenue-earning scheme: I hand over the cash at one of the currency changing desks before passport control, and get yet another page-filling stamp put in my passport. It takes no time at all.

I know I can get a 6-month, multiple entry visa from the Egyptian consulate, but I doubt this is possible on entry. It might damage the revenue flow ..